BACKGROUND. Through an RNAi synthetic lethal screen we have identified the protein SUMOylation pathway to be required for the viability of Ras mutant cancer cells. PURPOSE. In this project we aim to address the following questions: 1) the mechanism by which inhibition of SUMO ligases is synthetically lethal with the KRAS oncogene; 2) which cellular proteins are differentially SUMOylated in Ras mutant cells; and 3) How the changes in SUMOylation status of these proteins affect their function in the context of Ras mutant tumors. SIGNIFICANT MATERIALS AND METHODS. 1) shRNAs that target the SUMO E1 and E2 ligases and SUMO pathway proteins; 2) Stable cell lines expressing SUMO proteins and ligases; 3) mass-spectrometry methodology for identifying SUMOylated proteins in cell lysates. FY2013 ACCOMPLISHMENT. Continuing our effort from 2012, we have identified a number of proteins that are differentially SUMOylated between Ras mutant and WT cells. We are currently studying the functions of these SUMOylated proteins in KRAS mutant cell, particularly their role in KRAS driven transformation. We are also investigating how SUMOylation affects the activity of these proteins. We are currently preparing a manuscript for publication.